(1) Field of the Invention
The present invention relates to an Fe-Mn vibration damping alloy steel that has an excellent vibration damping capacity, and a method for making the Fe-Mn vibration damping alloy steel at a low production cost.
(2) Description of the Prior Art
In line with a trend for high-grade and high precision aircraft, ships, automotive vehicles and various machinery, vibration damping alloy is widely used in the many kinds of machine parts that are sources of vibration and noise. Study of vibration damping alloys has been lively because of the increase in demand for such alloys.
Vibration damping alloys developed and used so far are classified into following types: Fe-C-Si and Al-Zn which are of the composite type; Fe-Cr, Fe-Cr-Al and Co-Ni which are of the ferromagnetic type; Mg-Zr, Mg and Mg.sub.2 Ni which are of the dislocation type; and Mn-Cu, Cu-Al-Ni and Ni-Ti which are of the twin type. The above vibration damping alloys have excellent vibration damping capacities but have poor mechanical properties. Thus, the alloys cannot be used widely; and since they contain a lot of expensive elements, the production costs are high, limiting the industrial use of the alloys.
A solution of the above problem is disclosed in U.S. Pat. No. 5,290,372 (jong-Sul Choi, et al.). This patented alloy is an Fe-Mn (10 to 22%) vibration damping alloy steel having a partial martensitic structure. As a method for making the alloy, an Fe-Mn (10-22%) ingot is homogenized at 1000.degree. C. to 1300.degree. C. for 20 to 40 hours and hot-rolled. After solid solution treatment of the ingot at 900.degree. to 1100.degree. C. for 30 minutes to an hour, air cooling or water quenching is carried out to produce a partial epsilon martensite from the parent phase, austenite. This damping mechanism is entirely different from those of the conventional damping alloys, and has a characteristic of absorbing vibrational energy by movement of the .epsilon./.gamma. interface under external vibration stress. However, we have made an effort to further improve excellent vibration damping alloy steels and we succeeded in inventing a vibration damping alloy steel of the present invention.